1. Field of the Invention
The present invention relates to an ATM communication apparatus in an ATM communication network, and more particularly to an ATM communication apparatus suitable for controlling congestion in a communication network and a method of controlling a communication network using the ATM communication apparatus.
2. Description of the Related Art
As a conventional processing method of Enhanced Proportional Rate Control Algorithm (EPRCA) set forth in ATM Forum/94-0438R2 xe2x80x9cClosed-Loop Rate-Based Traffic Managementxe2x80x9d is known.
In this method, congestion detected in a network is notified to a communication apparatus using a resource management cell (RM cell), thereby to perform traffic control such as lowering a cell transmission speed so that the communication apparatus may evade the congestion. To be concrete, in this method, when a communication apparatus of a transmitting origin of a cell also sends out RM cells at appropriate intervals in addition to normal sending out of user cells for transmitting/receiving information among users, in case a congestion is generated in a certain apparatus in the network where the user cells pass therethrough, the congestion is notified to a communication terminal or a communication apparatus that is transmitting a user cell causing the congestion so as to perform such traffic control that the cell transmission speed is lowered in order to evade the congestion in the communication network by transmitting by return the RM cell to the apparatus of a transmitting origin after adding congestion information to the RM cell at a terminal point (a receiving side apparatus of the user cell) when the RM cell also passes through the apparatus and transmitted once to the terminal point together with the user cell, and a transmission band is utilized effectively while evading deterioration of the communication quality caused by the congestion in the network by controlling the cell transmission speed of the user cell sending origin.
Further, as another method of controlling a congestion, there is a method, such as disclosed in JP-A-7-183886, of lowering or suspending the cell transmission speed by notifying the communication apparatus that has transmitted the cell at a previous stage directly of generation of a congestion when the communication apparatus monitors a buffer provided on an input circuit side and detects the congestion. According to this method, since notification of a congestion ia made higher in speed and the quantity of cells inputted to the apparatus is controlled immediately, it is possible to evade a congestion even if the quantity of input buffers in the apparatus is small.
In the former among the methods of controlling ATM congestion described above, such operation is performed that RM cells inserted into a user cell flow at a fixed period are transmitted once to a receiving terminal or a communication apparatus which is an RM cell terminal point, congestion information is added to these RM cells and returned to an RM cell transmission terminal or a communication apparatus so as to detect the congestion information of the RM cells during the period from the time when a certain apparatus in the network falls into a congestion state to the time when the cell transmission speed in the user cell transmitting origin is lowered in order to evade the congestion. Thus, the congestion state is continued during that period. Namely, during the period until the communication apparatus of the transmitting origin starts traffic control, such a danger that the cells overflow and are lost (generation of cell discard) at a cell buffer for exchanging cells or the like is incurred. In order to evade such a phenomenon, it has been required to prepare a large quantity of cell buffers in a communication apparatus in a network so that cell discard is not generated in cell buffers even when the response time until the user cell transmission speed in an RM cell transmitting terminal or communication apparatus is lowered is long. The necessity for increasing buffers becomes more and more conspicuous when the network becomes large in scale, the communication apparatus is connected in multistages and propagation delay is increased (the response time gets longer), or the number of circuits to be processed is increased and the quantity of cells inputted to a communication apparatus is increased.
On the other hand, although the latter method for making congestion control higher in speed solves reduction of buffer quantity which is the subject in the former, it is not structured so as to investigate a transmitting origin in case a congestion is generated as a result that cells are inputted from a plurality of transmitting origins and to notify the transmitting origin of the congestion. Therefore, similarly to the case that communication apparatus are connected at multi-stages in a communication network, it occurs sometimes that such essential congestion evasion that the transmitting origin is controlled at the time of generation of congestion depending on the generation state of congestion such as a case that a congestion is generated in buffers on the output side of an exchange.
It is an object of the present invention to provide a method of controlling a congestion in which a method of controlling a congestion in a communication network such as described above has been improved and an ATM communication apparatus having a structure suitable for congestion control. To be concrete, it is an object to provide a method of controlling a congestion in a communication network capable of notifying a communication apparatus of a congestion generated in the communication network at a high speed and moreover capable of sending this notification surely to a communication apparatus of a cell transmitting origin which causes the generation of a congestion, and is capable of performing traffic control of the transmitting origin at the time of generation of a congestion, and an ATM communication apparatus for realizing the method of controlling a congestion.
It is another object of the present invention to provide a method of controlling a congestion or an ATM communication apparatus which, when any communication apparatus detects a congestion generated in the communication apparatus in an ATM communication network, is capable of notifying the congestion to a communication terminal or a communication apparatus that is sending out a cell causing generation of a congestion and shortening the response time until the cell transmission speed is lowered, and moreover, is capable of utilizing a transmission band effectively. Namely, the object is to provide a method of controlling a congestion and an ATM communication apparatus for notifying a communication terminal or a communication apparatus that is transmitting a user cell causing a congestion of the congestion surely at a high speed so as to perform traffic control such as lowering the cell transmission speed in order to evade the congestion in the communication network, and utilizing a transmission band effectively while evading deterioration of the communication quality caused by the congestion in the network by controlling the cell transmission speed of the user cell transmitting origin.
Further, it is another object of the present invention to provide an ATM communication apparatus suitable for a communication network performing congestion control and having a structure capable of evading cell loss or the like caused by generation of a congestion even if the buffer quantity of cell buffers prepared in respective communication apparatus is small.
Furthermore, it is still another object of the present invention to provide an ATM communication apparatus having a structure of detecting, when a congestion is detected, a congestion generating origin at a high speed and notifying of the congestion generating origin.
In order to solve the above-mentioned subjects, according to the present invention, a communication apparatus is provided with a detecting portion for detecting a congestion of the buffer, a transmitting origin analyzing portion for analyzing a transmitting origin for inputting a cell in a buffer in which a congestion is generated, a notifying cell generating portion for notifying of a congestion and a transmitting portion for transmitting the notifying cell to the cell transmitting origin in accordance with the result of analysis. Further, when it is detected that a congestion state is produced in an optional communication apparatus in a communication network, this communication apparatus identifies a communication apparatus of a transmitting origin inputting a cell which causes the congestion, and notifies the apparatus of the cell transmitting origin directly of the generation of the congestion. In the apparatus of the cell transmitting origin which has received this notification, traffic control such as lowering of the cell sending speed is executed immediately so as to perform congestion control of the communication network, thereby to prevent overflow of buffers and cell loss in the communication apparatus in which the congestion has been detected.
To be more concrete, an ATM communication apparatus used in a communication network composed of an interface for inputting/outputting an ATM cell, a cell buffer for storing cells for exchange thereof, and a control portion for performing control such as setting of the interface and the cell buffer is provided with a congestion cell buffer detecting portion for detecting a congestion state for each cell buffer, a transmitting origin retrieving portion for retrieving a cell transmitting origin which has inputted the cell into the cell buffer based on the identifier of the cell buffer in which the congestion state has been detected, and an RM cell generating portion for drawing up an RM cell notifying of congestion generation and transmitting an RM cell to a retrieved cell transmitting origin.
Besides, the above-mentioned cell transmitting origin retrieving portion is constituted of a cell buffer identifier pair received cell header information retrieving portion for retrieving a path identifier (VPI) or a connection identifier (VCI) of a header of a received cell which is a path identifier added at the time of receiving a cell inputted to a cell buffer which has reached a congestion state from identifiers of cell buffers. Further, the above-mentioned RM cell generating portion gives retrieved VPI or VCI to the header of the RM cell and transmits this RM cell to the transmitting origin which has transmitted a cell which has caused the congestion, and is constituted of a congestion notifying RM cell generating portion for generating an RM cell added with congestion information based on retrieved received cell header information and an output portion for sending the RM cell to a communication terminal or a communication apparatus which is transmitting a cell which causes the congestion. Further, a congestion cell buffer identifier notifying portion for notifying the retrieving portion and the RM cell generating portion of the output of the congestion cell buffer detecting portion using a signal of a format predetermined within an apparatus such as a maintenance cell may be provided inside the apparatus so that retrieval of a cell transmitting origin and RM cell transmission may be performed even for a communication apparatus having a structure in which a cell buffer, an interface and a control portion are separated from one another.